The BB rat develops insulin-dependent diabetes spontaneously. Susceptibility is inherited, and requires genes of the major histocompatibility complex (MHC) and T cell regulatory genes, including a lymphopenia of normal T cells. Infiltration of the pancreatic islets with lymphocytes and macrophages, and circulating anti-islet antibodies, are hallmarks of the disease which results in beta cell destruction. Many of these features are similar to those found in human Type I diabetes, one of the major causes of end stage renal disease. There is also a resemblance to the cell mediated destruction of renal tissue after allogeneic transplantation. Neither the cellular effector mechanisms related to pancreatic islet destruction in diabetic animals, nor the nature of cytotoxic effector cells in a transplanted rat kidney has been elucidated. We plan to apply techniques of cell culture, cloning, and molecular biology to answer questions on the nature and function of the autoimmune response in these lymphopenic rats. The focus will be on isolation of infiltrating lymphoid cells and classifying their phenotype by monoclonal antibodies specific for lymphocyte subsets, assessing their function as helper or cytotoxic cells on cell targets, or as non-specific effectors in ADCC or NK assays. Gene arrangements of the T cell receptors will be examined in Southern blots using cDNA probes for alpha, beta, gamma chains. Clones, expanded by islet antigen stimulation, allogeneic cells, or by mitogen, will be similarly examined and function correlated with T cell receptor and surface phenotype. We hope to identify the principal cell types associated with islet destruction, and contrast these with infiltrating cells obtained from the same BB strain rejecting renal transplants. Clones representing particular cells of interest will be subsequently used to induce anti-clonotypic antibodies of potential value in tracing the development of such clones during the evolution of disease. The expertise of three closely collaborating laboratories will be brought to bear on this project, initially using technologies already developed.